Description of the Related Art
An important feature in a desirable audio speaker design is sound quality. With the advent of mobile media players, such as smart phones, iPods®, and other devices, there has been an effort to develop small audio speakers, and in particular wireless speakers that receive a stream of digital information that is translated into sound via one or more speakers.
Typically, audio speakers include an enclosure and at least one sound transducer, or active driver speaker, having a diaphragm that produces sound waves by converting an electrical signal into mechanical motion of the driver diaphragm. Sound transducers, such as active driver speakers, typically generate sound waves by physically moving air at various frequencies. That is, an active driver speaker pushes and pulls a diaphragm in order to create periodic increases and decreases in air pressure, thus creating sound.
To create an audio speaker that has good sound quality and meets the use requirements of active portable lifestyles of today, it is desirable to form a speaker enclosure that is sealed to prevent ingress of dirt and water while the speaker is being used outdoors and exposed to accidents where the speaker may become submerged in water or drenched from water activity or rain. Traditional speaker designs may use port tubes which have no resistance to ingress.
FIG. 1 illustrates a conventional sealed active speaker assembly 100. The sealed active speaker assembly 100 includes a sealed enclosure 110 that includes a speaker 150 and a conventional amplifier assembly 90 that is typically positioned in an external region 102 that is outside the enclosure 110. The sealed enclosure 110 generally includes one or more walls 111 that enclose an internal region 101. The speaker 150 generally includes a diaphragm 152, a support frame 154, a surround 156, a voice coil 155, a pole piece 158, a permanent magnet 157, a dust cover 153 and a spider 159. During operation, the amplifier assembly 90 delivers a signal to the speaker 150, which causes the voice coil 155 to move the diaphragm 152 relative to the enclosure 110 (e.g., +/−Z-direction) due to the varying magnetic field generated by the coil 155 reacting to the fixed magnetic field generated by the permanent magnet 157. Typically, the diaphragm 152 has a desired movement range, which is related to a configuration of the frame 154, and has a mid-operation point. To minimize distortion, it is desired that the diaphragm 152 move outward and inward linearly with the bi-polar voltage applied by the amplifier 90. When in operation, the driven diaphragm 152 creates a pumping action as it moves in the plus and minus Z-directions, which affects the pressure in the internal region 101. The pressure variation in the internal region 101 can be very rapid as the speaker 150 generally delivers audible sounds at frequencies greater than 20 hertz (Hz), and the generated transient pressures in the internal region 101 can be as high as 100 psig.
It is common for conventional speaker manufacturers to strive to form a “sealed” speaker design. While it may be possible to manufacture a truly sealed speaker assembly that will not allow liquids or gases to pass in and out of the enclosure, this type of device can be very costly to manufacture. Most manufacturable consumer electronic designs today are not air tight, or even truly liquid tight. Moreover, trying to produce a fully sealed speaker design that has a desirable device yield during manufacturing and/or a desirable production cost is problematic. A conventional sealed speaker that is not completely liquid-tight or gas-tight will typically have short term and long term sound quality issues and may not be able to reliably meet typical water tight specifications required by consumer electronics manufacturers today. One common problem with conventional sealed enclosures relates to the monotonic increase or decrease in the pressure level within the enclosure due to the leak in the enclosure having a preferred leak direction “A” (FIG. 1). The creation of a leak that has a preferred leak direction is often created by the design of the seals 91 in the speaker enclosure. In some cases, the preferred leak direction acts as a one-way-valve that allows fluid movement in only one direction due to the design of seals used in the speaker assembly. The one way movement of fluid into or out of the internal region of the enclosure can, for example, cause a build up in positive or negative pressure that will alter the position of the active components in the speaker(s), such as the speaker diaphragm, and alter the range of motion of the diaphragm during operation.
As small and portable consumer electronic devices become more popular the need for a small liquid proof device that has good sound quality, has a low production cost and is manufacturable has increased in recent years. However, in the small speaker designs the volume of the internal region 101 is small compared to the amount of movement of the diaphragm 152 during normal operation. Thus, the pumping action of the diaphragm 152 during normal use in a small speaker can rapidly generate a large built-up internal pressure in the internal region 101 due to a leak in a conventional sealed speaker assembly. The built-up pressure in the internal region will cause the diaphragm's un-driven position to move from the desired mid-point of the diaphragm movement range and the mid-point of the coil driven region, which will limit the movement of the diaphragm, create distortion in the reproduction of the audio signal and create power inefficiencies. It has been found that by altering the position of the speaker diaphragm by only 5% from its nominal position will lead to distortion and a reduction in sound quality (SQ).
Also, even if a sealed speaker system had no parasitic leaks of any kind, then a pressure can build-up in the internal region 101 simply by a change in ambient temperature or altitude of the speaker system.
Therefore, there is need for a small enclosed and liquid tight sealed audio speaker design that provides a high-quality sound output and is easily manufactured. The devices, systems, and methods disclosed herein are designed to overcome these deficiencies.